1. Field of the Invention
The present invention relates to the thermoplastic elastomer blends of alpha-olefin polymers such as polypropylene or of their copolymers, such as copolymers of ethylene and propylene, with hydrogenated butadiene diblock copolymers having a 1,4-polybutadiene block and a 1,2-polybutadiene block, which blends require no curing or vulcanization to develop elastomeric properties. Moreover, the invention also relates to such blends partially cured.
2. Related Prior Art
The term "thermoplastic elastomer" has generally been applied to elastomers which can be readily molded and remolded, or otherwise processed and reprocessed, by common or conventional thermoplastic methods. The thermoplastic elastomers do not require vulcanization to develop their desired physical properties. Only a few types of such thermoplastic elastomers are known, such as the thermoplastic polyurethanes, the thermoplastic polyesters, for example those sold under the "Hytrel" brand name, the styrene block copolymers sold under the brand names of "Kraton" and "Solprene." Another thermoplastic elastomer is the blend of polypropylene and EPDM (ethylene-propylene-nonconjugated diene monomer) described in U.S. Pat. Nos. 3,758,743, 3,806,558 and 3,862,106.
It is known tht the blending of a polybutadiene rubber with an alpha-olefin polymer such as polypropylene results in a material with poor properties. It is most surprising therefore to find, as in the present invention, that the hydrogenation of butadiene block copolymers of high 1,4 and high 1,2 contents respectively effect such changes that the blending of such products with polymers and copolymers of alpha-olefins produce compatible products having good physical properties.